Research On Diagenesis And Analysis On Pores Diagenetic Evolution Of Sandstone Reservoirs Of The Upper Paleozoic, Ordos Basin

It is of important theoretical value and guiding significance of exploration arrangement for oil and natural gas, the choice of the favorable exploration targets to study diagenesis characteristics and pore structures based upon detailed description and observation of drilling cores, and various analytical and measurement methods including identification and quantitative statistics of thin sections under microscope, grain size analysis, analyses of X-ray diffraction (XRD), electron scan microscope (ESM), capillary pressure, cathodeluminescence, and measurement of homogeneous temperature for inclusions, and study pores diagenetic evolution history combined with burial and thermal evolution history of the Ordos Basin.After the comprehensive research of the diagenesis characteristics, pore structure characteristics, physical properties characteristics of the main gas bearing strata H 8 and Shan 1 reservoir of the upper palaeozoic formation, Ordos Basin, holds that:This study is Research shows that quartzrenite, sublitharenite and litharenite predominate in reservoir rocks. Diagenesis types include compaction, cementation, metasomatism and alteration, recrystallization and dissolution. The sandstones have experienced a diagenetic evolution from early diagenetic phase to later diagenetic phase. Pore spaces always occur as the combination form, and are mainly of secondary dissolution pores and kaolinite intercrystalline micopores. The primary intergranular pore takes a second place.The changes of the permeability are controlled by the development of the pores, and have a relationship to the size of pore throat and the connecting degree between pores and troats. Mechanical compaction and cementation were the main factor caused the loss of primary pores.Due to the buried condition differences between the east and west area, that the pore evolution characteristics under the diagenesis history are obviously different. The primary porosity of quartzrenite, sublitharenite and litharenite of western area are respectively 35.1%, 34.1% and 33.6%, when experienced a diagenetic evolution from early diagenetic phase A to later diagenetic phase B and C, their present porosity are respectively 9.2%, 10.6% and 9.7%. The primary porosity of sublitharenite and litharenite of eastern area are respectively 34.3% and 33.6%, and nowadays are 9.8% and 9.3%.The secondary pores of the sandstones were formed by the dissolution of the aluminosilicate, tuffaceous interstitial material and carbonate minerals effect by the carbonic acid and organic acid produced in late diagenesis stage. Hydrocarbon emplacement and tectonic thermal event act a positive role in the preservation of the primary pore and the formation of the secondary pores. There were two stages of hydrocarbon fluid injection between terminal middle jurassic and Late Early Cretaceous. Which characteristics separately as low temperature (80-110℃) low- middle matured hydrocarbon and higher temperature (120-140℃) high matured hydrocarbon.High -quality sandstone reservoirs are common controlled by material source and mother rock properties, diagenesis and diagenetical facies. Quartz sandstone was the sandstone type that benefit to the pore to be reserved and formation. The quartz overgrowth cementation mixture pores diagenetic facies, authigenic kaolinite cementation inter-crystal pores diagenetic facies, and clay matrix filling dissolution facies that distributing between the dense diagenetic facies are the most profitable diagenetic zones for developing high-quality reservoirs. Micro-fractures on one hand make the pores connect, improve the reservoir quality of the sandstones. On the other hand, act as the role that transporting petroleum.